The biochemical mechanisms by which mineralocorticoids exert their physiologic effects are not known. We have recently demonstrated that they induce the synthesis of "soluble" and "membrane" proteins in target cells. Characterizations of these induced proteins offer a means to gain a new understanding of the mechanism of action of steriod hormones and the means by which they regulate sodium transport. We have isolated these induced proteins from rat kidney and toad urinary bladder. We will now characterize them and determine whether they bind known inhibitors (ouabain, amiloride) or stimulators (vasopressin, cAMP) of sodium transport. We will also measure the Na ion -K ion-ATpase adenylate kinase and cAMP-stimulated protein kinase activities of these proteins.